The industry has many variations on piston seals using o-rings and polytetrafluoroethylene (PTFE) rings, sometimes referred to using the brand name TEFLON™. For example, various types and configurations of piston seals are disclosed in U.S. Pat. No. 7,815,195, U.S. Pat. No. 6,502,826, U.S. Pat. No. 6,129,358, U.S. Pat. No. 5,140,904, U.S. Pat. No. 5,082,295, U.S. Pat. No. 4,291,890, U.S. Pat. No. 4,109,921, and U.S. Pat. No. 3,592,164. While these piston seals appear to be appropriate for their intended purposes, none of these configurations provide a pressure activated low-leak seal with low actuation drag.
As best seen in FIG. 6, a prior known solenoid actuated hydraulic fluid valve 30 includes first and second valve members 30a, 30b, which are movable with respect to one another. One of the valve members 30a includes a groove 30c formed therein. A standard o-ring 32 is located within the groove 30c and biases a PTFE ring 34 into sealing engagement with the other valve member 30b. This sealing system uses the o-ring 32 to load a PTFE-based seal ring 34 against the inside diameter (ID) of the piston bore 36 defined by the second valve member 30b. 